This invention relates to a flexible energy absorbing system that can be used for a variety of purposes including garments to provide impact protection to the wearer. Known impact protection solutions currently available tend to fall into two types, namely a rigid exterior shell which can be uncomfortable to wear (e.g. roller blade or skateboard knee or elbow pads) or foam or foam laminate pads (e.g. inserts for ski clothing) which provide poor levels of protection.
There is therefore a need to provide an energy absorbing material which is both lightweight and flexible therefore being comfortable to wear while still being able to dissipate and absorb shock loads applied to so as to provide effective protection.
In my earlier published British patent application No. 2349798, a protective member is disclosed which uses an energy absorbing material which remains soft and flexible until it is subjected to an impact at which time it becomes rigid, said material being encapsulated in a flexible sealed envelope formed with one or more convolutions towards the direction of impact.
Considering an energy absorbing material alone, often impact, vibration or shock absorbing performance is related to the tensile strength of the parent material. This can be demonstrated in CE type tests namely EN1621-1 and EN1621-2 where the anvils are typically curved or domed. The impact performance of flexible energy absorbing materials is limited as they often bottom out and fracture at the impact site. Often the material is forced away from the contact area (impact site), leaving less energy absorbing material, usually leading to a reduced energy absorption and higher peak transmitted impact forces. The fracturing and movement of material away from the impact site is common in many materials but is especially important for flexible materials.
When we consider the area subjected to the highest load during an impact, typically a material will initially compress, in cellular products and foams this is sometimes referred to as the plateau region on a stress strain graph, further compressions leads to local densification, if total compression is limited to this then we have a normal recoverable energy absorbing system, further compression of the material “bottoms out” and the transmitted force increases and the material will start to fail by fracture. Further compression will break the material apart (fracture) moving material away from the contact site.
This application addresses ways to substantially prevent or stop the final fracture of material and keep material in the contact area.
The present invention therefore seeks to provide an energy absorbing material in which the movement of the material away from the contact site is reduced, stopped or even reversed, so that more material is introduced into the contact area during impact thereby improving energy management and absorption characteristics.
It has been found by the Applicant that materials according to the present invention exhibits considerably improved and surprising performance characteristics and impact resistance over known energy absorbing materials.
Accordingly, this application addresses how the energy absorption of an energy absorbing material may be improved by either adding a tensile layer to the energy absorbing material to provide local densification or restraint to the energy absorbing material, altering the geometry to give it a re-entrant configuration and/or introducing an active material such as a strain rate dependent material, preferably a dilatant material that exhibits chemical or silicone based dilatancy.
It will be appreciated that one or more of the improvements identified above may be used in combination with one or more of the other improvements to provide a further and often unexpected performance improvement.